Apparatus for retorting oil shale having a central axial hollow column



July 7, 1970 E. v. SCHULTE APPARATUS FOR RE'I'ORTING'OIL SHALE HAVING A CENTRAL AXIAL HOLLOW COLUMN 4 Sheets-Sheet 1 Filed Sept. 25, 1967 PQDQONQ TOR.

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APPARATUS FOR RETORTING OIL SHALE HAVING A CENTRAL AXIAL HOLLOW COLUMN Filed Sept. 25, 1967 4 Sheets-Sheet 2 n vswoa. 4 W000 Jove/4721 i vrroz/sx July 7, 1970 E. v. SCHULTE APPARATUS FOR RETORTING OIL SHALE HAVING A CENTRAL AXIAL HOLLOW COLUMN 4 Sheets-Sheet a Filed Sept. 25, 1967 1 YIENTOR.

awe/4775 BY 51% Z arr-012M501 his July 7, 1970 E. v. SCHULTE 3,519,539

APPARATUS FOR RETORTING OIL SHALE HAVING A 7 CENTRAL AXIAL HOLLOW COLUMN Filed Sept. 25, 19s? 4 SheetsSheet 4 FRESH 0/L SHALE V SEPA/ZA T02 PREHEA TING ZONE eooucr GAS AND OIL HEA TING ZONE AIR COOL ING ZONE REC YCLE 6/15 FIG. 10

SPENT O/L -SHALE ORE INVENTOR. EL WOOD V. SCHULTE BY g M5 Pillar/leg United States Patent O1 ifice 3,519,539 Patented July 7, 1970 US. Cl. 202117 18 Claims ABSTRACT OF THE DISCLOSURE Retorting of oil shale ore is carried out in a shaft-type furnace wherein: recycle gas is used to cool the spent oil shale ore in a cooling zone; air is mixed with the recycle gas and the mixture burns in a combustion zone above the cooling zone; and the gaseous products of combustion, including the kerogen derivatives that are driven from the oil shale ore, are removed from adjacent the top of the shaft furnace. The temperature within the retort furnace is controlled by apparatus within carefully defined limits. The gases and kerogen derivatives removed from the retort are separated and the combustible portion of gases, as recycle fuel gas, is fed back into the retort.

BACKGROUND OF THE INVENTION This invention relates to furnaces and, more particularly, to apparatus and the process for retorting oil shale, using vertical retort furnaces.

In many areas throughout the world, large quantities of oil shale are found. Oilshale is a form of marl that contans a bituminous material called kerogen. Kerogen varies in composition, consisting of approximately by weight 7783% carbon, 10% hydrogen, 15% oxygen and a small percentage of nitrogen. When the oil shale is heated, the kerogen is decomposed into derivatives such as oil, gas and other acidic and basic compounds.

Vertical shaft furnaces have been used heretofore to destructively distill the kerogen of the oil shale to obtain the valuable oils, gases, and other acidic and basic compounds. But, the equivalent available heretofore has not been suited to the efficient destructive distillation of the large quantities of oil shale ore that are necessary to make the recovery process economical. The present invention discloses apparatus that makes the destructive distillation of kerogen from oil shale ore economical and practical.

SUMMARY OF THE INVENTION According to the invention the temperatures at various vertically separated levels in an oil shale retorting furnace are monitored by temperature sensing instruments. A temperature profile controller correlates the temperature data, controls the flow of fuel gas and air into the furnace, and the rate of removal of the derivatives of kerogen driven off from the oil shale ore. Thus, the level of the raw oil shale ore moves downwardly and uniformly within the retort furnace and maximum recovery of liquid derivatives from the kerogen is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a schematic arrangement of an embodiment of the apparatus suitable for obtaining oil and gas from oil shale;

FIG. 2 is a detail of the top portion of the apparatus of FIG. 1;

FIG. 3 is a cross-sectional view of the gas take-off shown in FIG. 1;

FIG. 3A is a cross-sectional view of another embodiment of the gas take-off shown in FIG. 3;

FIG. 4 is an elevational view with sections broken out of a temperature sensor such as shown in FIG. 1;

FIG. 4A is an elevational view with sections broken out of another embodiment of the temperature sensor of FIG. 4;

FIG. 5 is an elevational view of another temperature sensor shown in FIG. 1;

FIG. 6 is a cross-sectional view of an air distributor shown in FIG. 1;

FIG. 7 is a sectional view along line VIIVII of FIG. 1;

FIG. 8 is a sectional view (in elevation) along line VIIIVIII of FIG. 7; and

FIG. 9 is an elevational view of another embodiment of the discharge structure of FIG. 8;

FIG. 9A is an elevational view of another embodiment of the structure of FIG. 9;

FIG. 10 is a simplified flow diagram for the furnace arrangement of FIG. 1;

FIG. 11 is a schematic sectional elevation of an embodiment of the furnace of the invention;

FIG. 12 is a vertical elevation of the furnace of FIG. 1 incorporating another embodiment of the support column;

FIG. 13 is a vertical sectional view of a portion of an embodiment of the furnace; and

FIG. 14 illustrates portions of the figures with the addition of an ultrasonic generator.

DETAILED DESCRIPTION FIG. 10 illustrates generally the process for decomposing the kerogen of oil shale to strip the resulting oil and gas from the oil shale particles. The raw oil shale which has been crushed and sized is fed into the top of a vertical kiln. The oil shale passes downwardly through a preheating zone where it is heated by the gases and vapors passing upwardly through the zone. Then the oil shale passes into a heating zone where the kerogen is decomposed and the gases and vapors released. The gases and vapors flow upwardly but oil shale, now the spent shale, continues downwardly and is removed at the bottom of the vertical shaft. Incoming recycle gases pass through the spent oil shale as the shale travels downwardly through a cooling zone where the shale is cooled and the recycle gases are heated.

The oil vapors and gases are removed at the top of the kiln near the location where the raw oil shale is fed into the kiln. The liquid and gaseous components are separated outside of the kiln. Some of the gases are recycled to the cooling zone of the kiln where the recycled gases are heated as they pass upwardly through the kiln and are burned at the heating zone to provide the heat to drive a further quantity of oil and gas from the oil shale.

The novel apparatus for obtaining product oil and gas by the destructive distillation of oil shale comprises generally a vertically elongated retort furnace 11, oil shale feed means 23 for introducing oil shale into the upper end of said furnace, product removal means 53, 55 for removing product oil and gas from the upper end of said furnace, means 89, 79 for introducing air to burn fuel gas introduced into the furnace at 101, 81 to supply the heat for said destructive distillation, a column 69 extending generally axially of said furnace for supporting in part selected ones of the foregoing means, and a grate 119 near the bottom of said furnace for controlling the discharge of oil shale from the furnace.

Referring to FIG. 1, apparatus suitable for carrying into practice the method of the invention includes a retorting furnace 11 having a cylindrical steel outer shell 13 which is lined (FIG. with a first inner layer of compressible insulating material 15, preferably in block form and a second and innermost layer 17 of refractory material, in the form of bricks or cast refractory (FIG. 5). The top end 19 of the metallic outer shell 13 is frustoconical in shape, and is also lined in the same manner as the main cylindrical shell 13. The frusto-conical top 19 merges with a cylindrical skirt portion 21 of a bell housing 23. The lower end of the outer shell 13 terminates in four frusto-conical members 43, each of which connects to a conventional rotary vane feeder mechanism 45. Around each rotary vane feeder 45 is a skirt 47 which is connected to the sloping side wall of the frusto-conical member 43 and which is open at the bottom.

The fresh or raw oil shale is introduced into the top of the furnace near the locus of removal of the valuable vapors and gases that have been produced in the kiln. Bell 23 enables the raw oil shale to be introduced into the top of the furnace without losing these valuable byproducts. Within the bell housing 23 are upper 25 and lower 27 conical bells that cooperate with upper 29 and lower 31 cones respectively to seal upper 33 and lower 35 material receiving chambers within the bell housing 23. The upper 25 and lower 27 bells are movable vertically by means of control rods 37, 39 respectively, whereby oil shale ore in the upper chamber 33 gravitates into the lower chamber 35 when the upper bell 25 is lowered away from the upper cone 29, and the lower bell 27 is in the closed position.

Prepared oil shale ore is fed to the upper chamber 33 from a conveyor belt 41 or other suitable materials handling apparatus, which may be operated in a coordinated manner with other apparatus of the system so that at least one of the ore receiving chambers 33, 35 is full of oil shale ore at all times.

So that the flow of oil shale particles will be uniform from the start of the flow of particles through the furnace, a plurality of coaxially disposed louver rings are arranged in circumferential echelon at the top of the furnace 11, within the frusto-conical top portion 19. In the illustrated embodiment of the invention, two such rings 49, 49a are shown (the upper ring 49a being smaller in diameter than the lower ring 49) but more than the two rings may be used, if desired. Such rings 49, 49a are held in fixed relation by brackets 51 attached to the inside of the frusto-conical shell 19. The rings are spaced apart both radially and vertically in such a way that the shale ore stock line in the frusto-conical portion 19 is spaced apart from the refractory 17. Since a gradient of particle sizes may exist, this arrangement of the louver rings 49, 49a keeps the larger pieces of shale ore from gravitating downwardly and outwardly so as to lie against the lining 17 of the furnace. Should the larger pieces of oil shale ore collect against the lining 17, most of the gases which supply the heat would tend to flow through the larger pieces of shale ore adjacent the furnace lining and a lesser amount of gases would flow through the more densely arranged smaller particles in the central region of the furnace. In this invention the flow tends to be uniform.

The gases and oil vapors which have evolved from the kerogen in the oil shale are removed at a location near the introduction of the raw oil shale. The gases and oil vapors thus in ascending in the furnace give up their heat to and thus preheat the oil shale which is descending. Ac-

cordingly, surrounding the top of the cylindrical shell 13, in spaced apart relation, is a manifold conduit 53 which is connected in communication with a plurality of spaced apart parallel horizontal gas olf-takes 55. Each off-take 55 is a U-shaped member (FIG. 3) having a rounded top and an open bottom. The U-shaped member 55 is supported in the refractory walls 15, 17. A fiat bottom closure member 57 Within the refractory lining 15, 17, extends outwardly of the shell 13 to join manifold 53, as indicated generally in FIG. 2, to prevent loss of the valuable gases and vapors to the atmosphere.

The gas off-takes 55 (FIG. 3) are advantageously so constructed that the ratio of height, H, to width, W, is not greater than five to one, and is preferably not less than one to two. The width, W, of each off-take, in a preferred embodiment of the invention, should not be greater than twelve inches in order to minimize the void space below the off-take, and to reduce the effect of segregation that may take place as the particles flow around the lower edges of the off-take. The distance between the walls of adjacent off-takes in a preferred embodiment should not exceed three feet for the reason that, when the shale ore gravitates around the off-take 55, the void space below the bottom edges of the off-take 55 may contain mostly the coarser particles of the shale ore, wherefore there'will be a flow path of lesser resistance for the hot gases, and an uneven distribution of heat throughout the shale ore bed results. Further, a spacing that is not greater than three feet is desired to maintain a uniform flow pattern of gases into the off-takes 55.

The manifold 53, in a preferred embodiment of the invention, will be of such size that the static pressure difference between diametrically opposite locations on the manifold will be not greater than six inches measured by a water column.

FIG. 3A illustrates the cross-sectional shape of another embodiment of an off-take 59; it being formed of spaced parallel side plates 61 with vaulted caps 63, 63a at the top that are maintained in spaced apart relation by spacers 65. The space between the vaulted caps 63, 63a is used to conduct either a cooling gaseous fluid, such as air, or a cooling liquid, such as water.

While bell 23 feeds the charged fresh oil shale into furnace 11 incrementally, the increments can be so spaced as to maintain an almost constant supply of fresh oil shale at the entrance to the furnace, thereby providing a substantially continuous flow of oil shale down the furnace to maintain the furnace in a steady-state condition. Louvres 49 tend to keep the charge uniform as it starts the movement down the furnace. The rounded tops of the off-takes 55 decrease resistance to the flow of oil shale downwardly through the furnace, and the Open bottoms decrease resistance of the gas to exhaustion from the furnace. In this manner, the charge can be fed into the top of the furnace without loss of valuable vapors and gases, the sensible heat can be extracted insofar as is practical from the by-product gases and vapors as quantities of heat to preheat the fresh shale oil, and the temperature difference between the gases and the oil shale is maintained at a minimum to give greater thermodynamic efficiency to the furnace.

From FIG. 2 it will be noticed that the plurality of gas off-takes 55 are centrally supported on a hollow rectangular horizontal support member 67. The top wall of the support member 67 is flat in way of each off-take 55, and supports an inverted angle-shaped cap 77 that extends between the walls of adjacent gas off-takes 55. This cap prevents shale ore from resting and accumulating on the top flat wall of the member 67.

The ends of support member 67 are mounted in the refractory lining 15, 17 and project outwardly beyond the furnace shell 13. Support member 67 is also supported near its mid length location by a hollow vertical conduit columnar member 69 that extends below the bottom of the furnace 11 and is supported upon a suitable foundation 71 (FIG. 1). The lower end of the vertical conduit member 69 communicates with a conduit 73 that conducts coolant, such as air, steam and the like, into the vertical conduit member 69. The gaseous coolant flows from conduit 73 through the hollow of vertical conduit member 69 into the horizontal support member 67 and through holes 75 (FIG. 2) in the bottom wall of the member 67 in the furnace. The coolant gases also" flow through the horizontal member 67 to the ambient atmosphere outside of the furnace 11. Thus, flexibility is achieved in control of the temperature at the top of the furnace.

Between the bottom and top of the furnace 11 are air distributors 79 and fuel gas distributors 81. Each of these distributors is in its own bank in separate horizontal lanes. The banks are comprised of a plurality of parallel ducts extending across the furnace. The respective air and fuel distributors 79, 81 are disposed in vertical spaced apart relation, with the air distributors 79 being located above the fuel distributors 81. Each bank of distributors 79, 81 is also supported near their mid length location by a horizontal hollow support member 67, which is mounted in the refractory walls 15, 17 and extends transversely of the furnace 11, as mentioned hereinbefore. The support member 67, as described before, is also supported near its mid length portion by the central vertical member 69, and is in fluid communication with the central vertical conduit member 69 through hole 75 in the lower wall of the conduit 67. The upper wall of conduit 67 has a hole 83 to admit cooling fluid to flow upward in the portion of the vertical member 69 extending above the conduit 67.

FIG. 6 illustrates a preferred form of horizontal air distributor 79. Each distributor comprises a horizontal cylindrical tubular conduit 85 having a plurality of diametrically opposed, horizontally spaced apart holes or orifices 87. Each conduit 85 communicates with an air manifold 89 which annularly surrounds the outer shell 13 of the furnace. Air under pressure is provided to manifold 89 from a suitable source such as a fan 91.

The area of the distributors 79, 81 is such that the pressure differential between opposed ends thereof is minimized; preferably, this pressure difference will not exceed 6 inches as measured by a Water column.

The air conduit 85 is fitted with a vaulted cover 93 (FIG. 6) that is welded to, or otherwise fluid tightly affixed to, the upper portion of conduit 85, and a box-type lower trough 95 that is fluid-tightly connected to the lower portion of the conduit 85. The upper vaulted cover 93 extends outwardly far enough so that the shale ore, because of its angle of repose, cannot obstruct the openings 87 in the conduit 85, and thereby obstruct the flow of gas from the distributors. The cover 93 forms with the conduit 85 a conduit 97 for cooling fluid, and the lower box-like trough 95 also forms a conduit 99 for cooling fluid. Both of the passages 97, '99 allow for the flow of a coolant such as air or water to cool the conduit 85. The cover and trough also strengthen the horizontal conduit 85, especially when it becomes heated while in service.

The fuel distributors 81 (FIG. 1) are generally of the same type as the air distributors 79. Since the fuel distributors are in the cooling zone of the furnace where temperatures are not as high as in the heating zone, cooling passages, such as 97, 99 of distributors 79 and the structural features that create these cooling passages may be omitted if desired. The distributors 81 are arranged in spaced apart horizontal rows, and each distributor 81 communicates with an annular fuel manifold 101 that encircles the lower portion of the funrace 11.

As described in the foregoing, a large number of parameters are present for the control of the pyrolysis of the oil shale as the oil shale proceeds down the furnace. Typical parameters, for example, are the flow of fresh oil shale, the rate of take-off of the by-product gas, the rate of addition of cooling gas, the rate of addition of air through the air distributor in the heating zone, and the rate of addition and kind of fuel supplied at the cooling zone. To monitor the conditions occurring within the furnace, temperature measuring instruments are located at various levels within the furnace and at varying radial locations. The temperature in accordance with this invention is regulated and determined at the interior of the furnace. Referring now to FIG. 4, for an embodiment of a temperature measuring instrument for ascertaining the temperature within the furnace a conduit 103 is mounted at one end to the central vertical support column 69, and is maintained in a horizontal attitude by means of diagonally arranged struts 107. The outer end 105 of the conduit 103 is closed, and a thermocouple 109, or other suitable temperature measuring instrument, resides in the conduit 103 near the closed end. Electrical wires 111 lead from the thermocouple 109 into the central vertical column 69 through the horizontal support members 67 and thence out of the furnace to a suitable temperature reading station.

A hole 110 with a removable cap 112 is provided on the central vertical column 69, in a location diametrically opposite the conduits 103, and 104 (FIGS. 4, 4A), to service and maintain the thermocouple elements 109, 1094.

Alternatively, the temperature measuring unit may comprise a closed end conduit 104 disposed in a downwardly sloping manner from column 69 and maintained in such an attitude by a diagonal strut 107a. A thermocouple 109a resides near the end of the conduit 104, and elec trical wires 111a lead from the thermocouple out of the furnace by way of the central column 69 and support member 67. Temperatures may be also measured at desired distances from the interior of the wall of shell 13 as illustrated at FIG. 5 by a closed end tube 113 which is mounted to the outer shell 13, and which projects horizontally through the refractory lining 15, 17 into the furnace 11. A thermocouple (not shown) resides in the tube 113 and electrical leads 115 from the thermocouple are connected in the temperature measuring or read-out equipment. The tube 113 is supported by a diagonal strut 117 in a horizontal attitude; but, of course, it may be supported at any convenient angular attitude in the same manner as tube 103a.

The rate at which the oil shale leaves the bottom of the furnace, and indirectly the rate of descent of the shale or residence time of the shale in the furnace is controlled by grate structure 119. The grate structure 119 (FIGS. 7 and 8) includes a plurality of spaced apart parallel horizontal diverter members 121 which are in the form of inverted structural angles. Each diverter member 121 is located vertically above a gap 123 between adjacent flat bottom support plates 125 that are fixed to shell 13 and arranged in spaced apart relation in a horizontal plane.

Plates 125 are supported by a plurality of vertical mutually perpendicularly arranged plate webs 133 which extend as chords from one side of the furnace shell 13 to the other side. The plate webs 133 form a grid that supports the horizontal plates 125 and the weight of the oil-shale ore in the furnace 11. The plate webs 133 may, of course, have other desirable shapes such as I-beams, channels, Z-bars and the like. Further, the grid members 133 may be hollow box beams that are fluidly cooled as by air or water.

On each support plate 125 is mounted a movable pusher bar 127 that is rectangular in cross section. Each pusher bar is connected to a plurality of actuating rods or drive shafts 129, that extend outwardly of the furnace shell 13, as shown in FIGS. 7 and 8. One of the fixed horizontal plates 125a, however, is mounted to the support column 69, and the pusher bar 12711 on that particular support plate 125a is connected to a yoke 130 that surrounds the central vertical column 69. In this manner, all of the pusher bars operate simultaneously when actuated by power sources, such as by hydraulic cylinders and pistons 131.

Those skilled in the art will recognize that the showing in FIG. 8 is not to scale, and that the sides of the diverter members 121 slope at such angles that the spent shale ore, having a natural angle of repose, will not dwell on the sloping sides of the diverters 121. Further, the diverters 121 are so located, with respect to the support plates 125 and pusher bars 127, that the spent shale ore will not gravitate continually down and around the diverters into the openings 123. The spent shale ore desirably rests on the bottom support plates 125 and is removed therefrom only by reciprocating the pusher bars 127, as mentioned hereinbefore.

FIGS. 9 and 9A illustrate other embodiments of apparatus for removing the spent shale ore; that is, the residue material after the kerogen derivative has been driven off as the oil shale ore descends in the furnace. The appaartus of FIG. 9 includes a pair of vertically spaced apart flapper valves or gates 135, 135a that are actuated by link mechanism 136, 136a, powered by push rods 137, 137a connected to a hydraulic cylinder-piston arrangement (not shown) or other suitable power mechanisms. Each flapper valve or gate closes the bottom of a hopper 138, 138a which receives spent shale material in sequential manner; that is, the spent shale material falls from the grate structure 119 (FIG. 8) into the hoppers 138, 138a. The spent shale material collected first in hopper 138 and, periodically, the flapper valve or gate 135 opens to drop the collected spent shale material into hopper 138a below. Then, periodically, but not necessarily simultaneously, the lower flapper valve or gate 135a opens to drop the collected spent shale material-onto a conveyor belt 139, as shown in FIGS. 1 and 8.

FIG. 9A illustrates another embodiment of flapper valve or gate. In this embodiment, the flapper valve or gate 140 is a conical bell that is similar to the conical bells 25, 27 of FIG. 1. Such bell valve or gate 140 cooperates with the walls of the hopper 138, and operates in response to movement of a link mechanism 136 powered by a push rod 137.

As an example of the operation of the apparatus in accordance with the invention, the conveyor belt 41 (FIG. 1) delivers fresh oil shale ore at a controlled rate of between 2 and 12 tons per day per square foot of crosssectional area of the furnace 11 into the upper chamber 33 of bell 31. The oil shale ore then gravitates into the lower chamber 35, and thence into the furnace proper when the bells 25, 27 are operated in sequence. Advantageously, the oil shale ore has been comminuted and sized so that the particles have a maximum and minimum size of between 2.0 inches and 0.1 inch.

While the furnace is operating, the gases produced in the retort and resulting from the decomposition of the kerogen are removed from the manifold 53 by way of conduit 143, a cooler condenser 145, a gas cleaner (wet or dry type) 147, and an exhaust fan 141. A po tion of the product gas flows through a flow controller 149 and into the manfold 101 through a conduit 151 as recycle fuel gas.

When desirable, an additional gas cleaner 165 may be connected by a conduit 167 in communication with the skirt 47 around each rotary feeder 45, to remove any traces of gas that may escape through the rotary feeders. A suction fan 169 communicates through conduit 171 with the gas cleaner 165 and, through a conduit 173, with an exhaust stack (not shown). Gas flowing in conduit 173 may be bled through conduit 175 and valve 177 into a product gas line 179 connected to the fan 141. Valve 181 in conduit 179 is automatically actuatable by the temperature profile controller 155 to maintain substantially atmospheric pressure at or adjacent the rotary feeders 45.

As the oil shale ore descends through the retort 11 at a desired rate, recycle gas (generally between 10,000

and 30,000 s.c.f. per ton of shale ore) flows through the flow controller 149 into the recycle gas manifold 101. Air is added by the air distributors 79. However, a deficiency of oxygen is present in the furnace; that is, a smaller quantity of air is present in the furnace than the amount that is theoretically required -to consume all of the gas. Sufficient air is added through manifold 89 and distributors 79 to maintain a temperature, immediately above the level of the air distributor 79, 89, in the range of 800 F. to 1400 F. Of course, the temperature at localized points in front of the holes 87 of the distributor may exceed 1400 F. As illustrated herein, a tempreature measuring thermocouple 109 is electrically connected to a temperature profile controller 155 that regulates the rate of air flow (preferably in the range of 2000 to 6000 s.c.f. per ton of oil shale ore) through an air control valve 157A to the manifold 89 and air distributor 79. To this end, controller 155 regulates the speed of the blower or fan 91 or the opening and closing of air control valve 157a or both to maintain the temperature in the retort at the air distributor level 79, at the desired temperature.

To conserve thermal energy, the sensible heat is recovered from the spent oil shale before the shale leaves the retort. This heat is recovered by flowing the fuel, herein the recycle gas, upwardly through the shale. T o accomplish this, a portion of the product gases pass through the flow controller 149 and conduit 151 to manifold 101 and to the recycle gas distributor 81. This flow is maintained at a rate suflicient to cool the spent shale material leaving the retort to a temperature in the range of F. to 400 F., as measured by the temperature measuring thermocouple in conduit 103d, located just below the recycle gas distributors 81, 101.

If the spent shale residue leaving the retort is cooler than desired, the temperature measured by the instrument in conduit 103d actuates the temperature profile controller 155. Ratio controller 1591) responds to a signal from the temperature profile controller to decrease the ratio of gas to air entering the manifold 101 by regulating valve 157b. If the temperature at level 103d is higher than desired, the temperature profile controller 155 actuates ratio controller 159]; so that valve 157b opens slightly, thereby allowing more recycle gas to enter the manifold 101. When, on the other hand, it is desired to raise slightly the temperature at level 103b, assuming that the temperature at level 103d is satisfactory, an adjustrnent may be made to the temperature profile controller 155 that will cause a slight increase in the rate of flow of air to the manifold 89 for the air distributors 79; ratio controller 159a being actuated to raise the recycle gas flow rate proportionately to maintain the same ratio of gas to air, and, thereby, automatically maintain substantially the same desired temperature at level 103d. If the slight change in gas and air flow rates, as related to the controlled shale ore rate passing through the retort, disturbs slightly the desired temperature at level 103a, the temperature profile controller 155 in response adjusts the recycle gas to air ratio controller 159]). The ratio controller 15% then opens or closes slightly the valve 157b, without disturbing appreciably the position of ratio controller 15%.

If, in any particular instance, the gas is recycled at a rate sufficiently high to cause the recycle gas valve 157b to fully open, or open so far that the ratio controller 1591) becomes partially noncontrolling, then the flow controller 149 may open the flow control valve 161 enough to return the ratio controller 15% to a state of active control over the rate of flow to the distributor 81, 101. If such maneuvering fails to achieve a stable controlled condition, then the temperature profile controller 155 may increase the speed of the gas recycle exhaust fan 141 to bring the ratio controllers back to a controlling state.

There will be cases where the temperature of the gases leaving gas off-takes 55, 53, as measured at level 103a,

or as measured by a thermocouple-type device 163 in conduit 143, will be desirably controlled at some maximum temperature. Whenever the temperature, as measured at 103a, or at 163, reaches this maximum value, then the temperature profile controller 155 will activate the ratio controller 15% and reset the ratio of recycle gas to air downward slightly.

Temperature profile controller 155 may also be used to regulate the temperature in the cooler-condenser 145 by regulating the rate of flow of cooling medium which may be either water or gas, to the cooler-condenser 145. Likewise, the temperature profile controller 155 may be used to control the degree of cleanliness of gas leaving the gas cleaner 147 by regulating the pressure differential across the gas cleaner, or by regulating the flow of water to the gas cleaner (when a wet unit is used), or by regulating both the pressure differential and the fluid flow rate.

In accordance with this invention the temperature profiles in the retort 11 for the maximum rate that oil shale ore can be retorted, optimum recovery of shale oil, obtaining optimum release of kerogen from the shale, and a minimum fuel consumption can be determined and the temperature profile controller 155 may be set to maintain the desired temperature profile as measured at various elevations without requiring control by a manual operator.

When desired, a temperature profile controller 155 may be used to maintain the same desired temperature profiles in a number of similar large vertical shaft retorts equipped with similar temperature profile measuring means.

The temperature measuring units described herein provide the needed accuracy for the temperature profile. Heretofore, it has been difficult to obtain temperature measurements within the bed, at the center or axis of the vertical retort or kiln, even for relatively small diameter shaft units. Heretofore when the temperature probe extended horizontally to the axis of the shaft from the shell or periphery of the retort, the pressure exerted on the probe unit, due to the friction and weight of descending solid particles, caused the relatively long probe unit (at the elevated temperatures) to bend downwardly out of the path of the shale and away from the center or axis and accurate temperatures could not be obtained. When the probe did bend down and away from the center or axis of the kiln, it would frequently break off and become inoperative and incapable of being used with a temperature controller to regulate and maintain the temperature of the bed at a particular elevation. Some attempts were made to measure temperatures within the bed, near the center or axis of the retort, by suspending a very long probe tube down into the bed from the top of the retort; but the long protective probe tube, extending from between the top of the retort and about midway between the top and bottom of the shale bed, became badly distorted and bent due to various pressures exerted against it by the descending solid particles so that it was not known definitely what temperature was being measured at that particular elevation in the bed.

In accordance with this invention a protector tube 113 (FIG. removes the measuring means sufficiently away from the lining of the retort at a preselected level or zone to indicate the temperatures near to, but not at, the lining. It provides a mean temperature measurement between the temperature profile near the axis of the shaft and the temperature profile near the lining, at a particular horizontal level in the shale bed. Thus in the invention, the temperature in the cross-sectional area of the retort, particularly at the elevation where liberation of shale oils and shale gases is taking place, is maintained at the desired temperature where the effective liberation of the oils and gases takes place. For example, if the temperature near the lining was about 800 F., while the temperature near the center or axis was about 1000 F., effective liberation of the oils does not occur near the lining. Then,

the temperature profile controller 155 may be readjusted to raise the temperature at that elevation from 1000 F. to 1100 F., which would also cause the temperature near the lining to rise by approximately an equal amount, i.e., from about the 800 F. to about 900 F. Such temperature near the lining would effect efficient liberation of the shale oils and gases without producing temperatures near the center that result in excessive undesirable cracking of valuable shale oils into decomposition gases.

Likewise, if the temperature at level 103b accidentally or by choice reached 2000 F., where a large percentage of the liberated shale oils become cracked to shale gases, and where the bed at this point might be approaching the temperature at which undesired clinker or fusion of shale occurs, then, the temperature measuring means 113 also indicates a temperature that approaches, but probably does not quite reach the same temperature. The temperature measuring means 113 would indicate that dangerously high temperatures prevailed at this elevation, and another measuring means 1031) at this elevation would confirm the accuracy of the first measuring. means 113. The temperature profile controller could then be adjusted to lower the temperature at this elevation to within the desirable range, that is, between about 800 F. and 1400 F.

When the recycle gases, rising through the retort 11, reach the distributors 79, the gases contact air issuing from orifices 87 (FIG. 6) and mix at temperatures that are above the ignition temperature of the gases. In fact, the temperatures at openings 87, as well as the temperatures in the voids between pieces of shale and in areas between and immediately above the air distributors 79, must remain above between about 1100 F. and 1300 F., until the oxygen in the air entering the bed through orifices 87 has been consumed to form CO and H 0. Immediately above the elevation where the ignition has taken place, the average temperature then drops back to the preferred temperature of between about 800 F. and 1400 F.

When a large retort is started up from a cold state, cold oil shale ore may be added to the retort up to an elevation at or slightly above the air distributors 79. Auxiliary burners (not normally used after the unit is operating and not shown here) may be inserted into spaces (not shown) below air distributors 79 and ignited, burning start-up gas such as natural gas and air, thereby obtaining substantially complete combustion of this auxiliary gas. The precaution should be taken, however, to burn only enough gas at these points so that the temperature at this level is above the ignition temperature of between about 1100 F. and about O F., and below the shale fusion temperature of between about 2000" F. and 2200" F.

Before the temperatures of the oil shale ore at these elevations reach the fusion temperatures, the filling of the remainder of the retort may be resumed. Almost simultaneously, the flow of recycle gas from storage through distributors 81, and the flow of air through distributors 79 at specified ratios and rates will be started. When these recycle gases, from recycle gas distributors 81 and air distributors 79 meet and mix at and adjacent the air distributors 79 and begin to burn at temperatures above the ignition temperature of the gases, the auxiliary start-up burners referred to herein may be turned off (and removed if desired) and combustion will be sustained by the normal recycle gas-air mixture.

If, in controlling the temperature at level 103b at between about 800 F. and 1400 F., the temperature of the shale ore should begin to approach between about 2000 F. and about 2200 F., where fusion of shale ore particles into small clumps begins to occur, such a condition is indicated by the presence of clumps in the spent shale ore discharging from the bottom of the retort. Then, the flame temperature should be lowered sufficiently to eliminate this fusion of shale by adding continuously and uniformly an inert gas to the air stream entering the retort through air distributors 79; being careful, however, always to maintain the temperature at this level above the ignition temperature of the air-gas mixture. This inert gas may be, for example, nitrogen, steam, products of combustion of the recycle gas, or a combination of these gases. The inert gas may be added continuously through a valve 183 in a conduit 185 connected to a source of supply. The valve 183 is actuated by the temperature profile controller, or other controller (not shown) to regulate the ratio of the flow of inert gas flowing through valve 183 to the flow of air flowing through valve 157a, thereby maintaining a desired flame temperature at the distributor 79.

The air and gases issuing from distributors 79 and 81 travel some vertical distance before they become uniformly distributedacross the whole cross-sectional area of the retort. For this reason, the vertical distances between air and gas distributors 79, 81 and between air distributors 79 and the product off-takes 55 must be sufiicient for uniformly distributing the gases. In the preferred embodiment, the distance between the distributors 79 and 81 and also between distributors 79 and gas and oil off-takes 55 is at least five feet and, preferably, more than ten feet.

As illustrated herein (FIG. 1) a wet or dry gas cleaner 147 is located in the recycle gas line between coolercondenser 145 and exhauster 141; but should gum-like deposits be produced in exhauster 141 to interfere with exhauster operation, wet or dry gas cleaner 147 may be located downstream or on the discharge side of exhauster 141. Then, the light shale oils, not totally removed in the cooler-condenser 145 (present as a fog in the gas) act as a lubricant in the exhauster 141 and prevent gum (or the like) deposits in the exhauster. When the exhauster is of the centrifugal type, a large percentage of oil particles are removed centrifugally from the gas at the exhauster. Sometimes, this secondary cleaning in the exhauster is sufiicient so that the wet or dry cleaner is not needed.

It is preferred to operate the flow measuring and controlling device 159b in the recycle gas line under substantially constant pressure. This may be accomplished by controlling the pressure between valves 1571) and 161 with a pressure controller (not shown).

Where water is scarce, it is possible to cool and condense vapors in the cooler-condenser 145 indirectly. This is done by sectionalizing the cooler-condenser 145, with the inlet or first section of the condenser-cooler partially cooling the recycle gas using air, and with the air that is preheated in the partial cooling process being used as the air needed at the distributors 79. Recirculated, cooled water may then be circulated through the outlet or downstream section of cooler-condenser to further cool the gas sufficiently (and preferably to below 175 F.) to obtain desired low power or steam consumption at exhauster 141.

The apparatus may be operated through a range of pressures. For example, sufiicient negative pressure may be carried at the top of retort 11 to maintain substantially atmospheric pressure continously inside of the retort, at the rotary discharge feeders 45 to minimize leakage of gas into or out from the retort. On the other hand, the discharge mechanisms 45 may be maintained tightly sealed, and the whole retort may be maintained at super atmospheric pressure with the top of the retort being maintained sutficiently above atmospheric pressure to prevent accidential leakage of air into the retort at the shale ore feed mechnisms 25, 27. Super atmospheric pressures, of course, eliminate the chance of an explosion, due to leakage of air into retort either via the green shale ore feeders at the top or the spent shale residue feeders at the bottom.

Grate mechanism 119 should be at a sufficient distance below the level of the recycle gas distributors 81 so as not to distrub the uniform descent of shale particles across the area of retort until the shale material has descended below the recycle gas distributor 81. On the other hand,

grate mechanism 119 should be located close to the recycle gas distributors to reduce the retort height. The distance between the grate mechanism 119 and distributors 81 usually will not exceed ten feet and, preferably, will be less than five feet.

In accordance with this invention, the use of the central column member, such as the member designated 69 in FIG. 1, permits flexibility in the design of the retort furnace in order to obtain maximum etficiency of operation. For example, when the gas flows are such that conical design of retort is desirable, a retort 111 can be readily made of a frusto-conical configuration such, for example, as illustrated in FIG. 11. The central vertical column 169 itself may be cylindrical, as the column 69 illustrated in FIG. 1 and have substantially the same cross-sectional area throughout the unit or it may have a varying cross section as in FIG. 12. In this instance, the column 269 may be frusto-conical in shape, as illustrated.

As has been discussed before, the hottest portion of the furnace is that portion immediately adjacent the air distributors 79, because the gas which has been preheated on its path from distributors 81 upwardly through the shale ignites and burns at this zone. Should this temperature rise to the shale fusion temperature, it is possible that some shale will agglomerate and bridge the distributors. Such fusion may cause a condition known as hang-up where the shale stops moving downwardly through the furnace and becomes lodged in the upper portion of the furnace 11.

In accordance with the embodiment of the invention illustrated in FIG. 13, a sleeve 203 with projecting arms 205 is supported by a collar 206 fixed to and surrounding the central vertical member 69. A motor 207 is secured to the outside of the shell 13 of the furnace 11 and, by way of both a drive shaft 209 extending through the sup port 67 and suitable gear arrangement 211, rotates the sleeve 203 and arms 205 in the furnace 11 to overcome any hang-up in the furnace.

As illustrated in FIG. 14, ultrasonic vibrations may be used, in conjunction with this furnace, to aid the uniform downward flow of oil shale ore and the escape of the product gas and vapors from the oil shale ore. A simple way of providing ultrasonic vibrations to the interior of the furnace is ilustrated in FIG. 14 where a siren 261 is installed in the air inlet 73 which provides cooling air to the furnace. As the air passes through the vanes of the siren 261, for example, the flow of air is changed to small increments of force of ultrasonic frequency which increments or puffs upwardly through the central column 69 as impact ultrasonic vibrations and thus, to the mass of oil shale in the interior of the furnace.

Those skilled in the art will be aware of the necessity of providing suificient slope to the walls so that the spent oil-shale ore will always descend into the feeders 45 and will not bridge or repose on the walls 43, and, thereby, clog the outlet of the retort furnace. In order to facilitate removal of the spent oil-shale ore, and in order to reduce the overall height of the retort furnace, a plurality of feeders are used, as suggested in the drawings. In some applications, however, only one discharge feeder may be used if preferred.

In some instances, a sensing device, not shown, may be installed on the wall 43 to detect the presence thereof of spent oil-shale ore build-up, and a signal from such sensing device may be directed to a controller governing the speed of the feeders 45 whereby they operate at a faster rate to remove the ore build-up.

The grate discharge mechanism 119 at the bottom of the retort furnace oscillates and is controlled by regulator 187 (FIG. 2), so that spent oil-shale ore discharges at such a rate (either increasingly or decreasingly in controlled stepped amounts) that the raw oil-shale ore in the skirt portion 21 is maintained, preferably, between low level 189 and high level 191. Preferably, the level should be at 193, about midway between levels 189, 191. The

13 rotary feeders 45 also operate at such a rate that the frusto-conical chute members 43 are maintained substantially empty.

If, at any time, the level of raw oil-shale ore falls below low level 189, to a level such as at 195, then an emergency control unit 197 sounds an alarm and either slows the rate of operation of the grate discharge mechanism 119, or stops the discharge mechanism for a period of time that is long enough to allow the level of raw oilshale ore to rise to level 193. Thereafter, the discharge mechanism resumes normal operation under control of the regulator 187.

If, on the other hand, a hang-up occurs in the retort, that interrupts the normal uniform downward movement of the oil-shale ore so that the raw oil-shale ore rises to a level 199, then another emergency control unit 201 sounds an alarm and either slows the raw shale-oil feeding conveyor belt 41 (FIG. 1), or stops it for a period of time that is sufiicient to dislodge the hang-up.

In such instances, the control unit 201 also regulates the bells 25, 27 so that no additional raw oil-shale ore may be discharged from the upper 33 and lower 35 chambers into the skirt 21. After the level of raw oil-shale ore returns to level 193, raw oil-shale ore feeding conveyor 41 and bells 25, 27 resume normal operation.

The bells 25, 27 are operated sequentially by the controller (not shown) that controls the rate of speed of the belt conveyor 41. Neither the upper 33 nor the lower 35 chambers is ever completely full, and it is preferred that the volume of the upper chamber 33 be not greater than the allowable working volume of the lower chamber 35.

In some applications, it is possible to obtain better control of the temperature throughout the mid-portion of the retort furnace, and thereby obtain more effective liberation of kerogen and the volatile shale-oil gases from the ore. This can be accomplished, without heating the oilshale ore particles to temperatures within the range (2000 to 2200 F.) in which fusion of the oil-shale ore particles takes place, by burning recycle gas in an auxiliary com bustion chamber of conventional design located outside of the retort furnace. The products of combustion produced in such an auxiliary combustion chamber will be at a temperature below the fusion temperature range and when such products of combustion contact the raw oilshale ore, clusters will not form.

When hot products of combustion are produced in such an external combustion chamber and conveyed to the internal distributors, such as distributor 79, '89, suitable temperature measuring means, such as the thermocouple 109 in device 103, may be used, and a signal from such temperature measuring device actuates a gas-air controller to feed the products of combustion at a proper temperature and at a proper rate so that the temperautre as measured by device 109 is within the desired limits.

The remainder of the recycle gas not used in the auxiliary combustion chamber would be added to the lowermost distributor 101, 81 near the bottom of the retort at a rate suflicient to maintain the temperature of the spent oilshale ore discharging from the retort in the range of between 100 and 400 F.

In a preferred embodiment of the invention, the lower bell 27 should be so located, with respect to the desired level 193 of shale ore in the skirt portion 21, that, when the lower bell 27 is opened, the shale ore falls in a path that meets the level 1193 at a locus about midway between the skirt wall 21 and the vertical central axis of the skirt portion 21.

Although the invention has been described herein with a certain degree of particularity, it is understood that the disclosure has been made as an example and that the scope of the invention is defined by what is hereinafter claimed.

What is claimed is:

'1. Apparatus for retorting oil shale ore containing kerogen comprising:

.(a) a vertical shaft furnace having an inlet at the top and one or more outlets at the bottom;

(b) gas sealing means at the top of said shaft furnace including an arrangement of movable members axially disposed one above the other to prevent leakage of gases from said furnace and providing an inlet for raw shale ore into said furnace;

(c) grate means adjacent the bottom of said furnace for supporting the weight of oil shale ore in said furnace and for the discharge of spent shale ore at a controllable rate;

(d) first distributor means above said grate for introducing fuel gas into said retort furnace, which gas cools the shale ore adjacent said distributor;

(e) second distributor means located in vertical spaced apart relation to and above said first distributor means for introducing ambient air into said shaft tfurnace, said air mixing with the fuel gas rising from said first distributor and burning in a combustion zone of said furnace adjacent said second distributor thereby heating said shale ore;

(f) third distributor means located in vertical spaced apart relation to and above said second distributor means and below said top gas sealing means;

.(g) horizontal tubular means supporting said first distributor;

(h) horizontal tubular means supporting said second distributor;

(i) horizontal tubular means supporting said third distributor;

(j) a vertical columnar tubular member communicating with and supporting each said horizontal support means;

(k) means to introduce into said vertical columnar member cooling gas which flows into each horizontal support member and cools the same;

(1) means to draw into said third distributor and to conduct away from said furnace the gases produced by burning said gas and air mixture andthe volatile derivatives of said kerogen which are liberated from the shale ore when subjected to the heat of said burning gas-air mixture;

.(m) valve means for controlling the flow of gases into said first distributor;

(11) valve means for controlling the flow of air into said second distributor;

(0) means for cooling and condensing the liquid derivatives of said kerogen and separating the gaseous derivatives from said liquid derivatives;

(p) means for removing said condensed liquid derivatives;

(q) means for removing and cleaning said gaseous derivatives;

(r) means for directing a portion of the gaseous derivatives through a flow control apparatus and into said first distributor;

.(s) a temperature profile controller apparatus;

(t) means connecting said temperature profile controller apparatus to said flow controller, said cooling and condensing means, each of said temperature sensing elements,

said valve means for controlling the flow of gases to said first distributor, said valve means for controlling the flow of air to said second distributor, and said means for drawing the derivatives of kerogen and other gaseous products into said third distributor and away from said fur nace, whereby the temperature at respective levels in said furnace is maintained within a preselected range of values for each respective level.

2. The structure of claim 11 including:

(a) means for actuating said grate to discharge spent shale ore at a controlled rate whereby the level of raw shale ore in said furnace moves downwardly uniformly and steadily; and

(b) means for discharging the spent shale ore from below said grate.

3. The structure of claim 2 wherein:

(a) said spent shale ore discharging means includes at least one rotary feeder.

4. The structure of claim 2 wherein:

(a) said spent shale ore discharging means includes a flapper valve and mechanism for actuating said flapper valve.

5. The structure of claim 4 including:

(a) a first compartment disposed beneath the bottom of said furnace with which said first flapper valve cooperates to close said compartment and retain spent shale ore therein;

(b) a second compartment located beneath said first compartment and a second flapper valve cooperating with said second compartment to close the bottom thereof;

(c) mechanism for actuating said second flapper valve;

and

(d) means for removing particulate matter from around the discharge of said flapper valves when they are open and when spent shale ore discharges through said valve.

6. The structure of claim 3 including:

(a) a tubular member annularly surrounding said rotary feeder; and

(b) means for removing particulate matter from said tubular conduit when said rotary feeder is operating.

7. The structure of claim 6 including:

(a) means for conducting discharged spent shale ore from adjacent the furnace discharge means.

8. The structure of claim 7 including:

(a) means for cleaning the dust laden air removed from the tubular conduit surrounding said rotary feeder.

9. In a vertical retorting furnace having therein a plurality of horizontal distributors for a fuel mixture that is burned in said furnace, each distributor having fluid conductive cooling passages, the improvement comprising:

(a) a vertical tubular member within said furnace supporting said distributors;

(b) means to flow cooling fluid through said vertical member;

(c) means to flow cooling fluid in said distributors to cool the same; and

(d) means to remove said cooling fluid from said distributors.

10. The invention of claim 9 including:

(a) a tubular member fluidly communicating with said vertical member and extending generally radially outward therefrom within said furnace;

(b) means maintaining said tubular member in such position;

(c) means closing the outer end of said tubular member;

(d) a thermocouple element resident in said tubular member; and

(e) lead wires connecting said thermocouple element to a temperature indicating device whereby the temperature within said furnace at the level therein where said temperature sensing device is located is indicated.

11. Apparatus for obtaining product oil and gas by the destructive distillation of oil shale comprising:

(a) a vertically elongated retort furnace;

(b) oil shale feed means for introducing oil shale into the upper end of said furnace;

(c) product removal means for removing product oil and gas from the upper end of said furnace;

(d) heating means for introducing fuel and oxygen into said furnace to supply the heat for said destructive distillation;

(e) a central axial hollow column in said furnace supporting said product removal and heating means; and

(f) a grate at the bottom of said furnace for controlling the discharge of oil shale from the furnace.

12. The apparatus of claim 11 wherein:

(a) said heating means comprises a fuel distributor and an air distributor, with (b) each heating means comprising a plurality of tubes of generally circular cross section extending horizontally across the furnace, the tubes having openings at the sides for the flow of gas and fuel therethrough; and including (c) a header for each distributor surrounding said furnace and communicating with said tubes; and

((1) individual covers for the top of each tube, said covers forming a conduit for the flow of coolant to protect said tubes.

13. The apparatus of claim 12 wherein:

(a) the fuel distributor is at a low elevation and the air distributor is at a high elevation whereby the fuel becomes heated in passing upward in the furnace from the fuel distributor and becomes ignited upon reaching the air distributor to supply heat for the destructive distillation of said oil shale.

14. The apparatus of claim 11 including:

(a) a plurality of temperature sensors projecting outwardly from said column at selected vertical intervals for providing a temperature profile for the internal mass in the furnace.

15. The apparatus of claim 14 including:

(a) means responsive to said temperature sensors for controlling said heating means.

16. The apparatus of claim 11 wherein:

(a) the product removal means comprises a plurality of off-takes extending across said furnace, each of said off-takes being of substantial height and width and having an upwardly extending top and an open bottom, the ratio of said height to width being between 5:1 and 1:2.

17. The apparatus of claim 10 including:

(a) an aperture in said vertical member at a location opposite said tubular member providing access for servicing and maintaining said thermocouple element in said tubular member; and

(b) a removable cap disposed over said aperture.

'18. The apparatus of claim 11 including:

(a) arms extending from said column and communicating with the interior of said hollow column, said arms supporting said product removal means and said heating means;-

(b) means for flowing a cooling fluid in the interior of said hollow column and in said arms; and wherein (c) said oil shale feed means comprises a plurality of superimposed chambers with internal bells separating one chamber from its next adjacent lower chamber and separating the lowermost chamber from the furnace interior; and including (d) a skirt connecting said oil shale feed means to said furnace;

(e) a plurality of rings disposed in said furnace coaxially of the said skirt with (i) each of said rings being displaced vertically from the other with the diameter of each lower ring being greater than the ring immediately above it; and with (ii) said rings having their loci within a conical surface whose angularity with the horizontal plane is greater than the angle of repose of the oil shale particles, whereby the larger pieces of oil shale are constrained against movement outwardly to separate from the smaller particles, and the tendency of the smaller particles to move toward the axis is interrupted by said column, and whereby the oil shale charge in 17 said furnace tends to move in laminar flow downwardly in said furnace;

(f) a level sensor for sensing the level of oil shale in said skirt;

(g) means responsive to said level sensor which actuates said grate to maintain a predetermined level of said oil shale in said skirt; and

(h) means for moving said bells to open said chambers in series.

References Cited UNITED STATES PATENTS 1,509,667 9/1924 Catlin 201-27 2,226,578 12/1940 Payne 202225 XR 1 8 7/1956 Reeves et al. 20127 9/ 1957 Williams 20l29 4/1964 Sanders 202-121 2/ 1967 McCleskey 266-25 FOREIGN PATENTS 3/ 1943 Switzerland. 11/ 1950 France.

WILBUR L. BASCOMB, JR., Primary Examiner D. EDWARDS, Assistant Examiner US. Cl. X.R. 

